If you want packability above all, this is your bag. It doesn’t have a gram of fat in features or material. By combining 900-fill down, vertical baffles with Insotect Flow technology (like the Marmot Plasma), a half-length zipper, and a trim fit (it’s tighter than the Plasma, but not quite as small as the Mountain Hardwear Mountain Speed), Sierra Designs created a bag that had our ultralight zealots raving. “It scrunches down even smaller than my puffy jacket!” exclaimed one.

Despite the compact packed size, the bag still lofts to six inches—plenty of insulation to keep one of our editors warm into the mid- to high 20s in the central Andes. (However, some testers complained that the lack of a full draft collar made it difficult to completely seal in heat when temps dropped to frigid levels.) Testers were impressed with the comfort and durability of the 10-denier nylon shell. “It’s silky smooth against the skin, keeps feathers inside where they belong, and is seemingly weightless,” says one. “After rolling around on granite slabs and snoozing on coarse sand to test the fabric’s durability, I have total confidence in this shell.” Bummer: The zipper snagged consistently. Also, the regular length was a tight squeeze for our 5’10” tester. $499; 1 lb. 12 oz.; 15°F; sierradesigns.comRedesigned for Spring 2012